On Mon, 19 Sep 2016, Jason Merrill wrote:
> > if (tree t = maybe_new_partial_specialization (type))
> > {
> > + if (processing_template_parmlist)
> > + {
> > + /* Some syntactically invalid code can confuse the compiler
> > into
> > + defining a specialization from inside a template parameter
> > + list. Bail out now so that we won't ICE later. */
> > + gcc_assert (seen_error ());
> > + return error_mark_node;
> > + }
>
> Rather than decide it's a specialization and then fail, let's avoid
> treating it as a specialization in the first place. I think we can
> add a processing_template_parmlist check at the top where we avoid
> trying to specialize lambdas.
>
> Jason
>
This works too. However I was playing around with the parser a bit and
noticed that the following also fixes the ICE. It makes no sense to try
to recover gracefully from a presumed missing "template <>" prefix when
processing_template_parmlist. This is what seems to be responsible for
creating the bogus specialization. Does this look OK or do you prefer
adjusting maybe_process_partial_specialization()?
gcc/cp/ChangeLog:
PR c++/77639
* parser.c (cp_parser_class_head): When
processing_template_parmlist, don't assume that a
class-head starts an explicit specialization.
gcc/testsuite/ChangeLog:
PR c++/77639
* g++.dg/template/error-recovery4.C: New test.
---
gcc/cp/parser.c | 1 +
gcc/testsuite/g++.dg/template/error-recovery4.C | 5 +++++
2 files changed, 6 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/template/error-recovery4.C
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index fb88021..c03b9c2 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -22025,6 +22025,7 @@ cp_parser_class_head (cp_parser* parser,
it is not, try to recover gracefully. */
if (at_namespace_scope_p ()
&& parser->num_template_parameter_lists == 0
+ && !processing_template_parmlist
&& template_id_p)
{
/* Build a location of this form:
diff --git a/gcc/testsuite/g++.dg/template/error-recovery4.C
b/gcc/testsuite/g++.dg/template/error-recovery4.C
new file mode 100644
index 0000000..1e52c6a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/error-recovery4.C
@@ -0,0 +1,5 @@
+// PR c++/77639
+
+template <class, int, class, int> struct B {};
+template <class T, int a, class U struct B<T, a, U, 1> {}; // { dg-error "" }
+B<int, 2, char, 1> i;
--
2.10.0.87.g1cd26dd
